1. Field of the Invention
The present invention relates to filter press machines for separating solids from liquids and, more particularly to improved polypropylene filter plates for use in such machines.
2. State-of-the-Art
Plate-type pressure filtration machines, typically called filter presses, are well known for separating solids from liquid slurries and for dewatering industrial and municipal wastes. A filter press is described, for instance, in U.S. Pat. No. 3,633,747 to Fismer. Recent efforts to enhance the efficiency of filter press machines have focussed upon increasing the effective filtering area presented by the individual filter plates of the press, thereby increasing the quantity of liquid processed per operating cycle of the machine.
One way to increase filtering area of a filter plate is, of course, to merely increase the size of the plate. However, large filter plates have increased susceptibility to deformation and breakage. For example, even small pressure differences across a large plate can cause the plate to crack.
In an effort to reduce breaking or deformation of large filter plates, workers in this art have suggested the installation of spacing elements, or stay bosses, in the space between adjacent filter plates to provide support in addition to that provided by the borders of the adjacent plates. It is also known to subdivide the filtering area of a plate into a number of filtering sectors, isolated from one another, by providing raised separating walls which extend across the filtering area between opposing borders of the plate. A filter plate which incorporates these features is disclosed in U.S. Pat. No. 3,615,015.
A disadvantage of filter plates having isolated filtering sectors is that individual liquid feed passages are required for each of the isolated sectors. These passages, in turn, reduce the effective filtering area of the plate, reduce the efficiency of the filter press, and increase the cost and complexity of the overall filtering system. Also, isolated filtering sectors, with their separate supply systems, enhance the possibility of pressure differences across a filter plate and, thus, enhance the probability of plate deformation and breakage.